1. Field of the Invention
The present invention is directed to a dosing device for the controlled deliver of a liquid from a reservoir, and in particular to such a device which is suitable for human implantation for delivering liquid medication.
2. Description of the Prior Art
A dosing device is disclosed in European Application 0 317 705 for injecting insulin from a reservoir into the body of a patient. This known device has a piston pump having a piston which can be moved through a stroke from a quiescent position to a position against a detent of a cylindrical housing surrounding the piston by means of an electromagnetic actuation system which can be switched on and off (energized and deenergized). A pump rate generator generates an "on signal" for energizing the electromagnetic actuation system for a time during each piston stroke. A detector generates an output signal when the piston strikes against the detent, the output signal being used in an evaluation means for generating an "off signal" for de-energizing the electromagnetic actuation system.
This known device is a battery operated implant, and in order to be able to monitor the course of the pump function, a detector is provided which indirectly acquires a signal corresponding to the motion course (such as an acceleration curve) of the piston, and detects when the piston strikes against the detent. The output signal generated by this detector is used for de-energizing the electromagnetic actuation system, so that it is assured that the pump is switched off at the end of each pump stroke, and further energy is thus not drawn from the battery.